Technique: wire preparation for a terminal block

Back to basics here guys.
I am referring to a terminal strip like this.
http://www.ledlight.dk/images/samlemuffe400x320.jpg
It may be 3 amp or 5 amp or something similar to that sort of low capacity.
The wire may be anything from wire which is thinner than bell wire up to approx 13 amp mains flex (1.5 mm^2).
----------------------------------- The QUESTION is this .... If you were using a terminal strip to connect some wires then how would you prepare the ends of the wire going into the terminal strip? It seems that there are few satisfactory ways. -----------------------------------
You can just strip back the insulation, twist if multi stranded, insert and screw down. However there is always a risk that some of the multi strands might break if the screw is tightened too much.
However if the wire is quite fine then you may have to fold the are wire back on itself. Maybe do that several times. But that does not come out cleanly unless the retaining screw is almost taken out.
You can add thickness to a fine wire by soldering/tinning the end of the wire before it goes in. But this adds a lot of fragility because where the solder ends is the point where the wire is likely to bend if it is moved around in use.
I've even seen people sticking in *insulated* wire and tightening the screw until it met the copper. This could work rather nicely but only if you can get the depth just right. It seems to me that chance plays far too large a part here.
The way I would love to do it is to get some sort of crimping tool and put a small brass collar over the wire and squeeze the collar on securely. The brass would be tough enough to resist the screw doing any real damage.
What do you find is the best?
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Zak wrote:

<snip>
I bought an assortemnt of sleeves and a crimping tool, to instrument cars,etc. Not only it solves the fraying/breaking wire problem, those sleeves also retain a little bit of the isolation , so that even if you have to move about the strip/circuit quite a lot ,wires do not tend to disconnect,and things look a lot more professional. You have 2 type of sleeves, metal only, or a small piece of coloured plastic extra. The last ones give most protection. (And you get coulour coding thrown it for free).
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That would be my favoured way of terminating the wires, as well. I seem to think that I've seen these things referred to in a catalogue, as " bootlace ferrules ". I'm never in favour of tinning wires prior to securing in a screwed terminal, for two reasons. First is the oxide layer that readily forms on the surface of solder, which may lead to a resistive joint in time. Second is creep of the soft solder, which over time leads to a loose screw. How many mains plugs have you opened, and found that the manufacturer pre-tinned leads, are virtually falling out of the plug pins, with the screws so loose, you could undo them with your fingers ?
Arfa
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Arfa Daily wrote:

I agree totally that soldered wires should not be put into any sort of screw terminal. I have learnt that the hard way: A long time ago I wired a lot of screw terminals after first soldering the ends of the wire, and a few years later I found that the terminals were loose and in some cases the wires had fallen out. If the wires were carrying current, they could get hot and start a fire. If they were for earthing etc. this could also be dangerous. I had to rewire the whole lot, without the solder.
I wonder if this will be the same with lead-free solder. I would rather not try it on anything important.
By the way you can buy screw terminals which have a flat piece of metal that clamps down on the wire instead of the screw itself. This avoids damage to the wire but the terminals cost a bit more. I would suggest buying the better terminals if this sort of thing interests you.
If you use crimp-on ferrules, make sure you have a really good crimp tool, because I have seen wires fall out of poorly crimped terminals. The one common characteristic of all good crimp tools, it seems to me, is that they cost at least a week's wages to buy.
Chris
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On Thu, 16 Mar 2006 22:17:23 GMT, "Arfa Daily"

FWIW, the Australian Wiring Rules prohibit the use of tinned wire in screw terminals for much the same reasons that you have outlined.
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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I use bootlace ferrules where ever possible (they are commonly used in the industry here). Would also try and use screw terminal blocks with built-in leaves that protect the screw head from the wire. Much better, especially if you want to redo the connection a few times.
I would never try and terminate soldered wires in a screw terminal block (it just isn't good practice).
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< Would also try and use screw terminal blocks with built-in leaves that protect the screw head from the wire. Much better, especially if you want to redo the connection a few times.>
That is the way it is done. This is a very efficient and common practice in the Control Industry.
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On 16 Mar 2006 14:21:39 -0800, snipped-for-privacy@electropar.co.nz Gave us:
snip

My prior argument in another thread in this group has been reinforced. I am redeemed!
Screw all the idiots that said it was OK too!
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Either just strip the wire and insert it or use some hollow pins on the end of the wires.
http://www.chromate.com/AgentCatalogWeb/Section%2020.pdf
And look on page 24 for them. YOu should also get their crimping tool.
I have seen and used thousands of the pins at work. Everything from a # 22 or so wire for a 4 to 20 ma circuit to larger wires. Some RTDs came in (probably 200 or more) with the same type of connectors. They had very small wire and were just put under the screws. On the other side we used the hollow pins or just the bare wire under the screws.
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use bootlace ferrule type crimps, and use the correct size connector strip for the size of cable you are using.
From the fact that you are quoting 1.5mm2 cable I would guess you are in the UK....All the main wholesalers stock ferrules and the correct crimping tools.
sQuick..
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No, the wire may NOT be in that range (thinner than bell wire). The terminal strip you show has a minimum wire size acceptance as well as a maximum.

That should read "There are few satisfactory ways".

If you strip it correctly, it will retain its original twist. Also, shear cutting should be used, NOT some lame pinch type snips.

Shouldn't be.

Bad practice, and likely that the wire is below the minimum spec for the connector block.

Bad practice. Should not be done... at all.

Such terminal strips are not meant to accept tinned ends of stranded wires. That is out of spec.

There is also a solder "creep" issue to worry about, and it is a significant issue.
http://en.wikipedia.org/wiki/Creep

The instance for having insulator in the screw to wire interface is too high. This is another practice that should be avoided.

Yes, brass creeps even less than copper, and far less than solder. In this case, one MAY use a smaller than spec'd wire size as well.
The tin plated crimp section of a cut off ring terminal (minus any insulation) would also be a good candidate for this procedure.

The right size solid wire is a straight insertion and clamp. The right size stranded wire with large gauge strands is a simple insert and clamp as well. Finer strands works, but starts to lean toward your last solution.
One should never apply a tinned stranded wire end in a screw clamp type terminal due to creepage issues.
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Snipped excellent response..
I agreed with you in the last thread, and I agree now. When you need reliability, use the correct size wire, apply it per the terminal strip manufacturer's recommendations, and don't use jury-rigged methods such as folding, soldering, etc.
I would point out to the OP that the terminal strip shown is a cheap type, which looks like the one Radio Shack sells for experimenters. It will work fine if the wire size is large enough. As others have mentioned, a better device with a clamping plate will accomodate a wider range of wire types and sizes, and might meet the requirements without the questionable methods. This is pretty much the norm for industrial control terminals.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
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Zak wrote:

From my view which has been formed over many years, use crimp lugs that capture the insulation inside the coloured pvc sleeve. I have had long periods of replacing bootlace sleeves that would appear to be a good system but in practice dont work out. It maybe they were not properly installed but IMHO they just are not reliable in the long run. Also as mentioned previously the connectors with the crush tab are a better proposition and are the "norm" for commercial installations. If possible use crimp lugs with flat sections that go into the connector strip. The professional crimpers made for each particular size of lug (Making a hexagonal compression) are the best but of course are expensive. It all depends where you are in the standard of installation :-)
--
Regards ......... Rheilly Phoull



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